Possibly the most "polished" game to date.
Gameplay: The gameplay is very good, just shy of being great. Coasting around Arkham City from rooftop to rooftop, crime-fighting all along the way, never gets old. Batman also gets to unlock numerous helpful gadgets preventing monotony. Combat can be a bit of a button masher, though, at least on normal difficulty. Enemies get skills and weapons as you progress through the game, keeping you somewhat honest, but they add only small amounts of strategy to your experience in combat. Bosses do better, as each may require taking advantage of their specific weaknesses (in one case: you must find five separate weaknesses.) Once the campaign is completed on normal difficulty, New Game Plus allows you to restart from the beginning with all of your upgrades to fight similarly upgraded enemies on a higher difficulty. This adds solid replay value. You can also continue from the end of the campaign without starting from the beginning, great for cleaning up loose ends. The addition of Catwoman adds more fun to the game, as she plays subtly differently, and has small adventures of her own to complete.
Story: The story is very entertaining, containing more enemies than all but the most dedicated of Batman fans could ever hope to be aware of. The primary enemies are more mainstream characters such as the Joker, Riddler, Two Face and Mr. Freeze. The addition of secondary fiends is accompanied by a background file for those of us who would otherwise never know who they are, or why they are there. Early in the game, when Batman can coast around the city at will, the numerous enemies and puzzles (placed by the Riddler) can seem a bit crammed and overwhelming. This is easily rectified as you become familiar with navigating the city and allow yourself to prioritize what you wish to accomplish. Voice acting is among the best in any game, although at times it can be a touch tone deaf. This is relatively minimal, and nothing to seriously complain about.
Graphics and Environment: The graphics are as sharp as any console game, and Arkham City is gorgeous. The open city is fairly large, active, and offers a near endless amount of enemies to beat up and riddles to solve. Unfortunately, the scope of the city is somewhat limited. Only around ten of the city's numerous buildings can be entered, meaning that it isn't rare to re-enter the same building for a different story or mission. While this made sense from a technical game-making standpoint, it results in highlighting these limitations.
Summation: This is a great game, one of the finest of this generation of the action genre. Its few limitations are overcome with a spectacular world to explore, solid voice acting and quality gameplay. My 2011 GotY.